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SqlDependency in an ASP.NET Application

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The example in this section shows how to use SqlDependency indirectly by leveraging the ASP.NET SqlCacheDependency object. The SqlCacheDependency object uses a SqlDependency to listen for notifications and correctly update the cache.

Note

The sample code assumes that you have enabled query notifications by executing the scripts in Enabling Query Notifications.

About the Sample Application

The sample application uses a single ASP.NET Web page to display product information from the AdventureWorks SQL Server database in a GridView control. When the page loads, the code writes the current time to a Label control. It then defines a SqlCacheDependency object and sets properties on the Cache object to store the cache data for up to three minutes. The code then connects to the database and retrieves the data. When the page is loaded and the application is running ASP.NET will retrieve data from the cache, which you can verify by noting that the time on the page does not change. If the data being monitored changes, ASP.NET invalidates the cache and repopulate the GridView control with fresh data, updating the time displayed in the Label control.

Creating the Sample Application

Follow these steps to create and run the sample application:

  1. Create a new ASP.NET Web site.

  2. Add a Label and a GridView control to the Default.aspx page.

  3. Open the page's class module and add the following directives:

    Option Strict On  
Option Explicit On  

Imports System.Data.SqlClient  

    using System.Data.SqlClient;  
using System.Web.Caching;

  4. Add the following code in the page's Page_Load event:

    protected void Page_Load(object sender, EventArgs e)
{
    Label1.Text = "Cache Refresh: " +
    DateTime.Now.ToLongTimeString();

    // Create a dependency connection to the database.
    SqlDependency.Start(GetConnectionString());

    using (SqlConnection connection =
        new SqlConnection(GetConnectionString()))
    {
        using (SqlCommand command =
            new SqlCommand(GetSQL(), connection))
        {
            SqlCacheDependency dependency =
                new SqlCacheDependency(command);
            // Refresh the cache after the number of minutes
            // listed below if a change does not occur.
            // This value could be stored in a configuration file.
            int numberOfMinutes = 3;
            DateTime expires =
                DateTime.Now.AddMinutes(numberOfMinutes);

            Response.Cache.SetExpires(expires);
            Response.Cache.SetCacheability(HttpCacheability.Public);
            Response.Cache.SetValidUntilExpires(true);

            Response.AddCacheDependency(dependency);

            connection.Open();

            GridView1.DataSource = command.ExecuteReader();
            GridView1.DataBind();
        }
    }
}

    Protected Sub Page_Load(ByVal sender As Object, _
   ByVal e As System.EventArgs) Handles Me.Load

    Label1.Text = "Cache Refresh: " & _
       Date.Now.ToLongTimeString()

    ' Create a dependency connection to the database
    SqlDependency.Start(GetConnectionString())

    Using connection As New SqlConnection(GetConnectionString())
        Using command As New SqlCommand(GetSQL(), connection)
            Dim dependency As New SqlCacheDependency(command)

            ' Refresh the cache after the number of minutes
            ' listed below if a change does not occur.
            ' This value could be stored in a configuration file.
            Dim numberOfMinutes As Integer = 3
            Dim expires As Date = _
                DateTime.Now.AddMinutes(numberOfMinutes)

            Response.Cache.SetExpires(expires)
            Response.Cache.SetCacheability(HttpCacheability.Public)
            Response.Cache.SetValidUntilExpires(True)

            Response.AddCacheDependency(dependency)

            connection.Open()

            GridView1.DataSource = command.ExecuteReader()
            GridView1.DataBind()
        End Using
    End Using
End Sub

  5. Add two helper methods, GetConnectionString and GetSQL. The connection string defined uses integrated security. You will need to verify that the account you are using has the necessary database permissions and that the sample database, AdventureWorks, has notifications enabled.

    private string GetConnectionString()
{
    // To avoid storing the connection string in your code,
    // you can retrieve it from a configuration file.
    return "Data Source=(local);Integrated Security=true;" +
      "Initial Catalog=AdventureWorks;";
}
private string GetSQL()
{
    return "SELECT Production.Product.ProductID, " +
    "Production.Product.Name, " +
    "Production.Location.Name AS Location, " +
    "Production.ProductInventory.Quantity " +
    "FROM Production.Product INNER JOIN " +
    "Production.ProductInventory " +
    "ON Production.Product.ProductID = " +
    "Production.ProductInventory.ProductID " +
    "INNER JOIN Production.Location " +
    "ON Production.ProductInventory.LocationID = " +
    "Production.Location.LocationID " +
    "WHERE ( Production.ProductInventory.Quantity <= 100 ) " +
    "ORDER BY Production.ProductInventory.Quantity, " +
    "Production.Product.Name;";
}

    Private Function GetConnectionString() As String
    ' To avoid storing the connection string in your code,
    ' you can retrieve it from a configuration file.

    Return "Data Source=(local);Integrated Security=true;" & _
     "Initial Catalog=AdventureWorks;"
End Function

Private Function GetSQL() As String
    Return "SELECT Production.Product.ProductID, " & _
    "Production.Product.Name, " & _
    "Production.Location.Name AS Location, " & _
    "Production.ProductInventory.Quantity " & _
    "FROM Production.Product INNER JOIN " & _
    "Production.ProductInventory " & _
    "ON Production.Product.ProductID = " & _
    "Production.ProductInventory.ProductID " & _
    "INNER JOIN Production.Location " & _
    "ON Production.ProductInventory.LocationID = " & _
    "Production.Location.LocationID " & _
    "WHERE ( Production.ProductInventory.Quantity <= 100) " & _
    "ORDER BY Production.ProductInventory.Quantity, " & _
    "Production.Product.Name;"
End Function

Testing the Application

The application caches the data displayed on the Web form and refreshes it every three minutes if there is no activity. If a change occurs to the database, the cache is refreshed immediately. Run the application from Visual Studio, which loads the page into the browser. The cache refresh time displayed indicates when the cache was last refreshed. Wait three minutes, and then refresh the page, causing a postback event to occur. Note that the time displayed on the page has changed. If you refresh the page in less than three minutes, the time displayed on the page will remain the same.

Now update the data in the database, using a Transact-SQL UPDATE command and refresh the page. The time displayed now indicates that the cache was refreshed with the new data from the database. Note that although the cache is updated, the time displayed on the page does not change until a postback event occurs.

Distributed cache synchronization using SQL Dependency

Some of the third-party distributed caches such as NCache provide support to synchronize the SQL database and cache using SQL Dependency. For more information and an example source code implementation, see Distributed cache SQL Dependency sample.

See also